Recently, highly efficient moving image compression methods using inter-frame correlation defined by MPEG2 (ITU-T H.262) or the like have been remarkably developing. These moving image compression methods are now used in the field of video cameras as well as other fields.
According to a moving image compression method used for a video camera, operation state information of the camera is used for compression in order to properly control the compression state of a moving image. For example, Patent Document No. 1 discloses such a technology. In addition to the technology disclosed by Patent Document No. 1, a great number of other related technologies have been studied and proposed. Many of such technologies have a common structure of controlling the filter in order to improve the image quality or to reduce the code amount. A basic structure thereof will be described below as a conventional example.
FIG. 9 shows a structure of a conventional moving image compression apparatus. Moving image data which is output from a camera section 101 including an optical system is transmitted via a pre-processing filter 102 to a moving image compression section 103, and a compressed moving image stream is output. Camera control information, which is separately output from the camera section 101, is transmitted to a filter control section 104. The filter control section 104 supplies a filter processing instruction to the pre-processing filter 102.
Hereinafter, an operation of the moving image compression apparatus of the conventional example shown in FIG. 9 will be described.
The camera section 101 performs digital signal processing on a signal of a moving image taken via the optical system, and outputs the resultant signal as moving image data, which is digital video image data. At this point, the camera section 101 executes many optical system controls and digital signal processing controls including focus control, zoom control, EV control on the diaphragm and shutter speed, correction control on the unintentional movement of the hands and the like. The camera section 101 outputs the control states as camera control information.
After the pre-processing filter 102 performs band restriction on the moving image data, the moving image compression section 103 performs compression processing on the moving image data based on the MPEG standards, and outputs the resultant data as a moving image stream. The filter control section 104 uses the camera control information to determine whether or not the current moving image has a characteristic which is difficult to be compressed by the MPEG2 format and will cause a relatively large number of compression strains. When it is determined that a relatively large number of compression strains will be generated, the filter control section 104 issues a filter processing instruction so as to more restrict the band of the filter. Upon receipt of the filter control instruction, the pre-processing filter 102 executes filter processing so as to more attenuate a high band component of the moving image data to be filtered. As a result, the information amount of the moving image data is reduced, and so an increase of the compression strains can be prevented.
Patent Document No. 1: PCT Japanese National-Phase Laid-Open Patent Publication No. 11-509701